The present invention relates generally to mechanical presses, and, in particular, to a mechanism utilized to adjust the spacing between the press bolster and slide to accurately control press shutheight.
Mechanical presses, such as stamping presses and drawing presses, include a frame structure having a crown and bed. A slide, which is supported within the frame for motion toward and away from the bed during operation, is typically driven by a crankshaft having a connecting arm connected to the slide. The slide is generally guided on the uprights of the press frame extending between the crown and the bed so that the parts of the die set remain in accurate registration as the slide reciprocates. Mechanical presses of this general type are widely used and vary substantially in size and available tonnage depending upon the intended use.
In prior art presses of this general type, a shutheight adjustment mechanism is often furnished such that the shutheight opening between the slide and the bolster or bed may be adjusted to accommodate various die sets. For example, the slide may be mounted by components which are essentially adjustable in length or position such that the slide may be shifted closer to or farther from the bolster. Alternatively, in designs such as disclosed in U.S. Pat. No. 3,858,432, the bolster of the press may be vertically shifted relative to the press bed such that the shutheight between the slide and bolster may be adjusted.
Operatively incorporated into their shutheight adjustment assemblies, many prior art mechanical presses include a plurality of bearings to reduce friction between the components which move during shutheight adjustment. Presses lacking these anti-friction bearings tend to require high adjustment torques due to sliding friction within the shutheight adjustment mechanism. However, these bearings are subjected to press stamping loads which can cause premature bearing failure. The bearing failure results in machine down time to perform the necessary replacement and maintenance. The stamping loads allowable in the press are also limited by the size or strength of the bearings. As the press load increases, the required size of the bearings increase. However, the larger size bearings tend to be less readily available from bearing suppliers.
Another shortcoming of anti-friction bearings commonly utilized in presses is that the bearings have fixed linear stiffness values. As the stamping loads applied to the bearing increase, the deflection of the bearing increases proportionally. Consequently, higher press loads may result in significant amounts of deflection that adversely impact press shutheight control.
In some shutheight adjustment mechanisms, hydraulic hold down pressure is utilized to lock the mechanism in a desired position. However, this pressure normally must be reduced or eliminated to adjust the shutheight, thereby adversely affecting the shutheight adjustment process.
Another shortcoming of many shutheight adjustment mechanisms pertains to the clearances provided between the component parts to facilitate their manufacture and assembly. These clearances increase the possible ranges of shutheight during press operation and may prevent the even transmission of pressure loads through the press. Uneven transmission of forces may cause particular parts, undergoing concentrated impact forces, to fail.
Thus, it would be desirable to provide a press with a shutheight adjustment assembly which may be used to overcome these shortcomings of the prior art.